Calculate 32-bit insert/s limit

[vinniefalco]

Can 32-bit reach > 4GB/s insert? If so then code needs to be audited for 32-bit limit correctness (i.e. when std::size_t is 32 bit).

[vinniefalco]

It looks like the bulk insert test crashes on 32-bit systems, because the high insert throughput exhausts available memory.